Dispensing various types of viscous materials can be challenging due to changes in the viscosity of the material. Some types of materials, such as polyurethane reactive or PUR adhesives, tend to increase in viscosity by curing slightly over the time period of their use. For example, the viscous PUR material contained in a heated dispensing syringe may change during the time period that it is exposed to a manufacturing environment. For PUR adhesives, exposure to moisture or humidity in the environment will cause the viscosity to change due to slight curing since this material is designed to react in the presence of moisture or humidity. Various other materials exhibit changing viscosity over time such a two component adhesive systems that are pre-mixed and loaded into a dispenser such as a syringe or other materials used in various applications such as adhesives or sealants that thicken over time for any reason.
Pressurized air or fluid is often used to force the PUR adhesive from the syringe with or without the aid of a piston-type element. Assuming the air pressure supplied to the syringe stays the same, and the viscosity of the material increases, less material will be dispensed over time as the viscosity of the material increases. For this reason, the dispensed amount can become lower and lower over time and may even deviate from specifications or desired parameters. Other types of dispensers may exhibit similar challenges.